Psychologist Roger Shepard, a professor at both Harvard and Stanford, published a book called Mind Sights in 1990. This book has been described as “…both stimulating to the eye and provocative to the mind.” It also happens to feature one of the most famous and classic optical illusions of all time. While most people know it simply as the “impossible elephant”, the actual title of the work is “L’egs-istential Quandary”. How many legs can you count on this elephant?

Regarding his L’egs-istential Quandary image, Roger Shepard writes the following in Mind Sights:

“The elephant…belongs to a class of objects that are truly impossible in that the object itself cannot be globally segregated from the nonobject or background. Parts of the object (in this case the elephant’s legs) become the background, and vice versa.”